There is not a time of year when you can't use  nymphs to catch trout, panfish and and even bass. Some nymphs, like Hellgrammites, the larval form of dobsonflies,  may live as long as three years in the water before they hatch into winged adults. This means that at any given time there are these nymphs present in streams, lakes and ponds. This realistic looking imitation  was designed by Dave Whitlock. These are tied on 6x long  Mustad  streamer hooks with the hook bent slightly so the fly rides hook point up. Size #4  6X long shank hook length is about 1.5 inches, #4 3X long hook is 1.25 inch.